diff --git a/ISectionProperties/IConcreteProperties.cs b/ISectionProperties/IConcreteProperties.cs
index 8128de7..b92c449 100644
--- a/ISectionProperties/IConcreteProperties.cs
+++ b/ISectionProperties/IConcreteProperties.cs
@@ -4,12 +4,12 @@ namespace MagmaWorks.Taxonomy.Sections.SectionProperties
 {
     public interface IConcreteProperties : ISectionProperties
     {
-        Length EffectiveDepthY { get; }
-        Length EffectiveDepthZ { get; }
-        Area CompressionReinforcementAreaY { get; }
-        Area CompressionReinforcementAreaZ { get; }
-        Area TensionReinforcementAreaY { get; }
-        Area TensionReinforcementAreaZ { get; }
+        Area ConcreteArea { get; }
+        Area LongitudinalReinforcementArea { get; }
         Area ShearReinforcementArea { get; }
+        IConcreteSectionProperties TensionNegativeYProperties { get; }
+        IConcreteSectionProperties TensionPositiveYProperties { get; }
+        IConcreteSectionProperties TensionNegativeZProperties { get; }
+        IConcreteSectionProperties TensionPositiveZProperties { get; }
     }
 }
diff --git a/ISectionProperties/IConcreteSectionProperties.cs b/ISectionProperties/IConcreteSectionProperties.cs
new file mode 100644
index 0000000..584ac60
--- /dev/null
+++ b/ISectionProperties/IConcreteSectionProperties.cs
@@ -0,0 +1,13 @@
+using OasysUnits;
+
+namespace MagmaWorks.Taxonomy.Sections.SectionProperties
+{
+    public interface IConcreteSectionProperties
+    {
+        Length EffectiveDepth { get; }
+        Length EffectiveWidth { get; }
+        Area CompressionReinforcementArea { get; }
+        Area TensionReinforcementArea { get; }
+        Area ConcreteArea { get; }
+    }
+}
diff --git a/SectionProperties/SectionProperties.cs b/SectionProperties/SectionProperties.cs
index 77038ff..a60363e 100644
--- a/SectionProperties/SectionProperties.cs
+++ b/SectionProperties/SectionProperties.cs
@@ -37,7 +37,7 @@ public Length RadiusOfGyrationZz
         private Length? _radiusOfGyrationZz;
         private IProfile _profile;
 
-        private SectionProperties() { }
+        internal SectionProperties() { }
 
         public SectionProperties(ISection section) : this(section.Profile) { }